1. Field of the Invention
This invention relates in general to methods for making semiconductor devices especially those having a passivation layer such as a mesa transistor or diode.
2. Description of the Prior Art
Semiconductor devices sometimes have surfaces which are not level and have grooves or ridges formed therein which result in sharp corners or edges being formed on the surface of the semiconductor device. Passivation layers such as silicon dioxide layers or SIPOS layers such as described in copending application Ser. No. 561,532 filed Mar. 24, 1975 entitled "Semiconductor Device" in which the inventors are Takeshi Matsushita et al, are utilized to protect the junction area in the substrate and in making a mesa transistor or diode it is necessary to form windows in the passivation layer so as to attach an electrical contact through the window. In the prior art photo-etching processes it has been known to make such windows through the passivation layer, however, such process is not feasible with the mesa transistors or diodes which have an uneven surface because the photoresist layer tends to become too thin at the corners or edges and thus when etching occurs the passivation layer is not protected by the thin photoresist layer and is removed which is undesirable. The photoresist is applied to the surface of a semiconductor wafer as it is rotated by a spinner at high speed on a mandrel and becomes very thin on sharp corners of a surface of a transistor with grooves and ridges, and, thus, the passivation layer using such prior art techniques would be undesirably removed using such conventional methods.